<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>flex 容器定义</title>
</head>

<body>
    <pre>
.container {
    display: flex;
    flex-direction: column;
}
</pre>
    <div class="container">
        flex 容器定义
    </div>
</body>

<style>
    * {
        margin: 0;
        padding: 0;
    }

    .container {
        display: flex;
        flex-direction: column;
    }
</style>

</html>